JP2001347364A - Porous filter for molding molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous filter for filtering inclusions contained in the molten metal when molding the molten metal mainly consisting of iron, nickel and cobalt. SOLUTION: This porous filter for molding the molten metal which is formed of a sintered body of silica powder is suitable for the molten alloy mainly consisting of one kind, or two or more kinds of metals selected among iron, nickel and cobalt. The amount of the amorphous component in the silica component constituting the filter is >=80%. This filter is most suitable for the molten metal having the composition consisting of >=60% in total iron, nickel and cobalt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of casting industry in which molten metal is poured into a mold and the molten metal is solidified to obtain a casting. The present invention relates to a porous filter for use.

[0002]

2. Description of the Related Art Conventionally, in the foundry industry, a method has been used in which various molten metals are poured into a mold and solidified to obtain a shape. This method has a great advantage that products having complicated shapes can be easily obtained. Generally, first, a casting metal material is melted at a high temperature to obtain a molten metal. The mold is a sand mold, and is provided with a gate and a runner for pouring the mold. Since the molten metal contains inclusions (slag, etc.) that adversely affect the performance of the casting, it is necessary to remove these before the molten metal enters the mold. A porous ceramic filter having heat resistance is used for removing inclusions in the molten metal. The porous ceramic filter is installed at the bottom of the gate or the runner attached to the casting mold.

[0003] The first function of the filter for casting molten metal is to trap inclusions such as slag in the molten metal and prevent the inclusion in the casting. For this reason, it is necessary to select a filter having an optimum gap depending on the type of the molten metal. Further, the second function of the filter is to rectify the flow of the molten metal. When the molten metal flows directly from the gate into the runner, the flow of the molten metal is turbulent. It becomes a defect.
Therefore, the turbulent molten metal is rectified by installing the filter at the bottom of the gate or on the runner, so that the sand mold shaving phenomenon can be prevented. It should be noted that the filter is almost completely clogged with inclusions and solidified metal after one pouring operation, and is generally discarded.

[0004] A filter patent is disclosed in Japanese Patent Application Laid-Open No.
No. 14 describes a method for producing a ceramic foam using a polyurethane foam. Also, Japanese Unexamined Patent Publication No.
No. 111817 describes a ceramic porous body as a filter material for molten metal. Further, as a production method and a ceramic material, JP-A-63-265880 describes a method for producing a porous sintered body having continuous pores, and as a material for a molten metal filter, alumina, zirconia, zircon, cordierite, Mullite, silica, aluminum titanate and the like are mentioned as materials.

At present, various ceramic filters have been researched and developed, and are already commercially available. Typical filter materials are alumina, zirconia, cordierite, silicon carbide-glass, and graphite. The criteria for selecting the filter material are generally determined by the type of the molten metal.
For example, graphite, alumina, and cordierite are used in the case of low melting point molten aluminum and aluminum alloy.

On the other hand, a zirconia filter and a cordierite filter are used for a molten metal mainly composed of iron, nickel, and cobalt having a high melting temperature. Zirconia has excellent corrosion resistance to molten metal and slag containing these metal components. However, the filter made of zirconia is excellent in corrosion resistance, but has a coefficient of thermal expansion of about 10 × 10 ⁻⁶ / ° C., which is much higher than other filter materials. For this reason, even if a porous body having only a dense skeleton is manufactured, when it comes into contact with a high-temperature molten metal due to its high linear thermal expansion coefficient, intense thermal stress is generated, and the porous body structure is destroyed. Therefore, as a countermeasure, the particle diameter constituting the skeleton of the porous body is made coarse, etc. However, since the mechanical strength of the porous body is low and the sinterability is reduced by the amount of the coarse particles, the sinterability is reduced.
Requires high temperature sintering of 00 ° C or higher. For this reason, the production cost is much higher than cordierite or the like, but at present, it is used because there is no material superior to zirconia. However, a zirconia filter having a very large coefficient of linear thermal expansion has a fundamental problem that cracks occur in a part of the skeleton of the porous body due to thermal shock depending on the working conditions and the cracks are mixed into the casting.

[0007] Cordierite filters have a certain degree of thermal shock resistance because cordierite has a relatively low coefficient of linear thermal expansion. However, a high melting point molten metal mainly composed of iron, nickel, and cobalt requires not only thermal shock resistance but also high-temperature deformability, high-temperature strength, and corrosion resistance.
In the case of cordierite, there are problems with low strength and corrosion resistance, and in many cases, performance is inferior to zirconia filters.

Further, in a commercially available ceramic filter such as zirconia, a portion of the molten metal is temporarily solidified immediately after coming into contact with the molten metal, causing instantaneous clogging of the filter. The clogging is such that the total amount of heat of the molten metal is enormous compared to that of the filter, so that over time, the entire filter warms and the solidified metal is re-melted. However, during re-melting, a high pressure is applied to the filter by the molten metal having a high specific gravity, so that there is a problem that a part of the porous ceramic skeleton constituting the filter is easily damaged. When the filter is no longer clogged under high pressure, the molten metal starts passing through the filter at once. This is not desirable from the viewpoint of rectifying the turbulence of the molten metal, which is the original purpose,
As a practical matter, the sand mold may be shaved and mixed into the mold. No ceramic porous filter has been put into practical use that has excellent corrosion resistance and thermal shock resistance against molten metals with high melting temperatures, especially iron, nickel, and cobalt-based molten metals, and hardly causes initial solidification. Is the current situation.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has excellent heat shock resistance and corrosion resistance in a casting process using a molten metal containing iron, cobalt, and nickel as main components. It is an object of the present invention to provide a highly efficient and highly reliable porous filter for molten metal, which has almost no instantaneous clogging of the molten metal at the beginning of molten metal filtration.

[0010]

The inventor of the present invention has made intensive studies on the above problems, and as a result, a porous filter for molten metal which can be used practically by employing the following means (1) and (2). We found that we could provide. (1) A porous filter for casting a molten metal made of a sintered body of silica powder, wherein the molten metal contains one or more metals selected from iron, nickel and cobalt as main components. A filter for a molten metal, comprising: a molten alloy having an amorphous component in the silica component of 80% or more. (2) The filter for molten metal according to (1), wherein the total of iron, nickel, and cobalt in the molten metal is 60% or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The porous filter for molten metal of the present invention comprises a sintered body of silica powder. Silica can be crystallographically classified into quartz, cristobalite, tridymite, and amorphous (silica glass). Among them, amorphous silica has the lowest linear thermal expansion coefficient, and has a smaller linear thermal expansion coefficient than other oxide and non-oxide ceramics, and a temperature difference of 1000 ° C. or more from the viewpoint of thermal shock resistance. It is the most suitable material for the filter for molten metal exposed to water.

In the sintered body of the silica powder of the present invention, the amount of the amorphous component in the silica component is preferably 80% or more. When the amount of the amorphous component is less than 80%, that is, when the amount of the crystalline silica component is increased to 20% or more, the thermal shock resistance of the filter rapidly decreases. The crystalline silica component here refers to the above-mentioned quartz, cristobalite, and tridymite. In particular, the linear thermal expansion coefficient of cristobalite is high, and when the cristobalite crystal is contained in an amount exceeding approximately 20% in the silica sintered body, The thermal shock resistance is reduced, and cracks tend to occur in a part of the skeleton forming the porous body. Although the coefficient of linear thermal expansion varies depending on the type of crystalline silica, the filter of the present invention generally has a coefficient of linear thermal expansion of about 3.5 × 10
It is desirable that the temperature be lower than ⁻⁶ / ° C. The amount of amorphous silica is calculated by extracting a part of the filter material, pulverizing the material, quantifying the amount of crystalline silica by powder X-ray diffraction, and subtracting the amount of crystal from 100% of the total amount. The crystal amount is measured three times in consideration of the measurement error, and the average value is defined as the crystal amount. The calculation method is preferably an internal standard method, but an external standard method can also be used as appropriate. The linear thermal expansion coefficient is measured by a general method, and the linear thermal expansion coefficient from room temperature to 800 ° C. is calculated.

[0013] By controlling the amount of amorphous silica in this way, in the filtration of a molten alloy composed of one or more metal components selected from iron, nickel and cobalt, non-metal components in the silica component can be filtered. When the amount of the crystalline component is 80% or more, no crack is generated in the skeleton of the porous body constituting the filter, and no small ceramic pieces are mixed into the cast body.

Furthermore, the material of the filter installed between the mold and the gate is made of commercially available cordierite, mullite,
When it is made of alumina, zirconia or a composite thereof, as described above, there is a phenomenon that the molten metal causes a temporary solidification phenomenon immediately after pouring, and passes through the filter at a stretch after a lapse of time. This is probably because the reaction between the surface layer of the filter material and the molten metal is endothermic.

On the other hand, in the sintered body of the silica powder of the present invention,
It has a feature that solidification of the molten metal in the initial stage of pouring is unlikely to occur. That is, for example, the reaction with molten iron is represented by the following chemical reaction formula. SiO ₂ + 2Fe + (O) = Si + Fe ₂ O ₃ This reaction is caused by silica, iron and coexisting oxygen, and is accompanied by heat generation. In other words, it is considered that since the molten iron generates heat when it comes into contact with the silica, the molten metal does not absorb heat, so that the initial solidification phenomenon hardly occurs. A similar reaction system can be considered for nickel and cobalt. That is, the porous filter for molten metal casting comprising the sintered body of the silica powder of the present invention can prevent solidification of the molten metal at the beginning of pouring by using a filter made of a silica-based sintered body.

At the same time, of the crystal components of the siliceous sintered body,
By setting the amorphous silica content to 80% or more, especially iron,
It is also possible to achieve prevention of cracks during filtration of a molten metal composed of an alloy containing one or more metals selected from nickel and cobalt as main components, and prevention of mixing of small ceramic pieces. These two components are the most important features of the present invention. In particular, the effect of the siliceous sintered body of the present invention is exerted more in an alloy composition having a larger total of iron, nickel, and cobalt, and is preferably one, two, or more selected from iron, nickel, and cobalt. If the metal component is a molten metal having an alloy composition of 60% or more, the filter performance is further improved.

The filter of the present invention can be manufactured by means of molding and firing ordinary porous ceramics.
For example, a silica powder slurry is adhered to urethane foam, and a porous body is obtained by firing, or a so-called urethane foam method, or a highly viscous paste containing an organic binder is thinly extruded, and this is voided by a geometric movement. Examples of the method include a method of laminating so as to have, a method of manufacturing a honeycomb in which silica powder and an organic binder are kneaded, extruded into a honeycomb shape by a vacuum extruder, and fired, and a casting method using a core. The present invention is a filter for molten metal obtained by sintering silica powder, and is not limited by a method of forming and firing the filter. In any case, it is necessary to select a raw material so that the amount of amorphous silica in the sintered body is 80% or more, and to form and fire it.

The sintered body composed of the obtained silica powder is 3
Even if it has a three-dimensional skeleton or has a honeycomb shape, the structure is not only a dense body or a fired body having closed pores, but also a structure in which coarse particles and fine particles are fused, or a skeleton is porous. It also includes those that are quality structures.

[0019]

EXAMPLES (Example 1) Melt composition: Gray cast iron (FC300) Pouring temperature: 145
After preparing a slurry composed of silica powder, water, an organic binder and a dispersant, the slurry is impregnated into a flexible polyurethane foam (100 × 100 × 20 mm thickness) having a three-dimensional skeleton, dried at 120 ° C., and then dried at 600 ° C. After incineration of the organic material by sintering, the mixture was sintered. By changing the sintering conditions, the amorphous content becomes 100, 96, 93, 86, 80, 76, 65.
% Of various types of siliceous sintered bodies were obtained. The crystalline silica was cristobalite. Table 1 shows the linear thermal expansion coefficient of each sintered body. For comparison, a cordierite filter and a zirconia filter were also prepared by the same method, and the filter performance was compared.

The percentage of amorphous in Table 1 indicates a weight ratio. The linear thermal expansion coefficient is a value from normal temperature to 800 ° C. The filtering performance refers to the presence or absence of cracks, partial detachment of the skeleton, and the like in the casting and the filter after the injection of the molten metal. The initial solidification refers to the approximate time (seconds) during which the molten metal solidifies and stagnates after injection. Numbers in the table, 1 to 7 are porous filters for molten metal casting made of a sintered body of silica powder;
Is a comparative example.

The siliceous sintered body of No. 1 had good initial solidification properties, but had a low amorphous silica content of 65% (composition containing 35% cristobalite).
The linear thermal expansion coefficient of the raw material increased, cracks occurred in the filter frame during filtration, and a part of the material was broken, so that the unfiltered molten metal was cast into a mold. Inclusions in the molten metal were scattered in the casting, and it was difficult to use the casting as a casting.

In the silica sintered body of No. 2, the crack resistance was improved because the amount of amorphous silica was 76%, which was larger than that of No. 1, but the number of tests was increased to 10 times. About one time, the uncrosslinked portion of the filter skeleton was broken, and a phenomenon was observed that the uncrosslinked portion was mixed into the casting as small pieces. This casting was also difficult to use due to internal defects.

In Nos. 3 to 7, which are the scope of the present invention, there was no cracking, detachment of small pieces and incorporation into the cast at 50 times of pouring tests, and the initial solidification time was much higher than that of Comparative Example. It was a short time, and the molten metal was smoothly poured into the mold. In addition, since there was an error in the initial solidification measurement, it appeared that pouring started almost instantaneously in the filter made of the silica sintered body of the present invention.

On the other hand, in cordierite No. 8, detachment of small pieces and mixing of castings were recognized about twice in 10 times in terms of filtration performance. This is because the coefficient of linear thermal expansion of cordierite is slightly higher than that of the silica sintered body of the present invention, and the skeleton constituting the porous filter cannot withstand the high pressure due to the initial solidification phenomenon in terms of strength.

The zirconia filter of No. 9 has excellent corrosion resistance, but the initial solidification time is about twice as long as that of the silica sintered body of the present invention, and the sand particles are frequently contained in the cast body about once every 15 times. The mixing phenomenon and the mixing of minute pieces into the casting were observed. This is thought to be due to the fact that the skeletal strength of the zirconia filter was higher than that of cordierite, but part of the sand mold was cut off by high-pressure pouring that occurred after the initial solidification. As described above, the performance and reliability of the porous filter for molten metal casting made of a siliceous sintered body as shown in the present embodiment are excellently different from other commercially available filters.

[0026]

[Table 1]

(Example 2) Melt composition: SCH12 (Fe-18Cr-8Ni) A casting test was conducted in the same manner as in Example 1. Also in this example, in the filters of Nos. 3 to 6, there was almost no solidification in the early stage of pouring, and no mixing of ceramic pieces and sand particles in the casting was observed at all, showing good results.

(Example 3) Melt composition: SCH22 (Fe-20Ni-25Cr)

Example 4 Melt composition: SKH5 (Fe-4Cr-20W-1.3V)
-16.5Co)

(Example 5) Melt composition: Fe-13Cr-0.2C

The molten metal compositions shown in Examples 3 to 5 are also the same as the molten metal composition of Example 1 and have the number 3 to 4 which are within the scope of the present invention.
7 is an extremely short initial solidification time of less than 1 second on average, and the cordierite and zirconia porous filters for molten casting are both 2 to 3 seconds. Cost me.

[0032]

The porous filter for molten metal of the present invention has the following advantages. 1) The initial solidification phenomenon at the time of casting can be shortened, and the molten metal filtration performance is excellent. 2) It is possible to prevent contamination of the casting due to breakage of the filter. 3) Cast products can be obtained with high quality and high yield.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D019 AA03 BA05 BA06 BB06 BD01 CB04 CB06 4E014 NA08 4G030 AA37 BA25 GA09

Claims (2)

[Claims] 1. A porous filter for casting molten metal comprising a sintered body of silica powder, wherein the molten metal contains one or more metals selected from iron, nickel and cobalt as main components. A filter for a molten metal, comprising: a molten alloy having an amorphous component in the silica component of 80% or more. 2. The filter for molten metal according to claim 1, wherein the total of iron, nickel and cobalt in the molten metal is 60% or more.